In the field of work machines, particularly those machines which perform digging or loading functions such as excavators, backhoe loaders, and front shovels, the work implements are generally manually controlled with two or more operator controls in addition to other machine function controls. The manual control system often includes foot pedals as well as hand operated levers. There are several areas in which these types of implement control schemes can be improved to alleviate operator stress and fatigue resulting from the manipulation of multiple levers and foot pedals. For example, a machine operator is required to possess a relatively high degree of expertise to manipulate and coordinate the multitude of control levers and foot pedals proficiently. To become productive an inexperienced operator requires a long training period to become familiar with the controls and associated functions.
Some manufacturers recognize the disadvantages of having too many control levers and have adapted a two-lever control scheme as the norm. Generally, two vertically mounted joysticks share the task of controlling the linkages (boom, stick, and bucket) of the work implement. For example, Caterpillar excavators employ one joystick for stick and swing control, and another joystick for boom and bucket control. However, the two-lever control scheme presently used in the industry may still be improved to provide for better productivity.
One disadvantage of the joysticks of this type is the use of contacting switches. For example, joystick contacting switches are used to control direction of movement. However, such switches are subject to wear, necessitating switch replacement or repair. Thus, the long term cost of such joysticks is quite high. Further, when a joystick is not operating properly, the machine cannot be used. This "down-time" greatly adds unacceptable burdens to the machine owner/leasor due to time restrictions on most jobs.
Several attempts have been made to overcome the problems of contact-type joysticks. For example, the non-contacting control-handle discussed in U.S Pat. No. 4,434,412 and the control signal generator discussed in U.S. Pat. No. 4,654,576 each teach the use of inductive sensors for detecting the displacement of a control shaft from a neutral position. However, such inductive sensors are susceptible to electromagnetic interference, are complex to manufacture, and require expensive drive circuitry for operation.
Another type of non-contacting joystick is discussed in U.S. Pat. No. 4,489,303, which teaches the use of Hall effect devices to detect the position of the control shaft from a neutral position. However, Hall effect devices have problems similar to the inductive sensors discussed above. Further, this particular joystick arrangement is limited to detecting only a limited number of discrete positions of the control shaft. For example, a magnet disposed on the control shaft can actuate only one of the Hall effect switches at any particular time. Thus the resulting positional information has poor resolution leading to poor accuracy.
Further, the above devices require complex spring arrangements to "center" the control shaft to the neutral position. Over long periods of use the spring force of these complex spring arrangements may reduce, which may lead to poor repeatability. Additionally, each of the described devices only provide for two-axis detection. Thus, more than one device is needed to control the work implement in the above described machines.
The present invention is directed to overcoming one or more of the problems as set forth above.